Electromagnetic friction clutch for a vehicle door

ABSTRACT

The invention relates to an electromagnetic friction clutch for arrangement within a drive train connecting a drive motor and a vehicle door. The vehicle door is reliably held in any intermediate position when a clutch is disconnected. To preserve the ability to carry out a manual emergency actuation of the vehicle door, a compression spring is provided acting upon an armature disk of the clutch in the axial direction in such a way that, with the clutch in the disconnected state, the armature disk is pressed against the frictional lining of a rotor part with a force which is sufficient to ensure that the vehicle door remains reliably in position. During a subsequent manual actuation of the vehicle door, the frictional connection between armature disk and frictional lining can be overcome.

The invention relates to an electromagnetic friction clutch forarrangement within a drive train connecting a drive motor and a vehicledoor or vehicle flap (tailgate, drive motor hood, etc.).

In motor vehicles with an automatically actuable vehicle door or vehicleflap (hereafter also designated in summary simply as a vehicle door),the vehicle door is closed or opened, for example, by the driver of thevehicle as a result of a corresponding actuation of a switch provided inthe instrument panel. For this purpose, the switching signal generatedby the switch acts on an electronic control device which itselfgenerates electrical control signals for activating an electric motorwhich, in turn, then pivots or displaces the vehicle door via afollowing gear unit and further transmission elements.

These known motor vehicles have the disadvantage, inter alia, that, whenthe vehicle door is pressed shut manually, a high resistance has to beovercome on account of the gear unit or electric motor operativelyconnected to the vehicle door and an increased wear of these componentsoccurs.

To avoid wear of this kind, an automatically actuable vehicle door hasalready been proposed, in which the motor or the gear unit following themotor can be decoupled by means of an electromagnetic clutch from thedrive shaft actuating the vehicle door, so that, with the clutch in thedisconnected state, a manual actuation of the vehicle door is possible,without the movement of the latter being inhibited by the structuralunits (for example, electric motor or intermediate gear unit) arrangedon the drive shaft of the clutch.

Electromagnetic clutches of this type are designed, as a rule, asfriction clutches and therefore comprise a rotor part which is providedwith a friction lining and is connected fixedly in terms of rotation toa first shaft and which has arranged on its side facing away from thefriction lining an electrical coil, and an armature disk which isconnected fixedly in terms of rotation, but axially displaceably, to asecond shaft and which, with the clutch in the connected state, is drawnagainst the friction lining of the rotor part of the first shaft andmakes a frictional connection between the two shafts. With the clutch inthe disconnected state, the armature disk and the rotor part are pressedapart from one another by means of a spring, so that there is an exactlypredetermined gap-like clearance between the armature disk and thefriction lining.

The abovementioned vehicle doors have the disadvantage, however, that,in the dead state, because of the open clutch, the vehicle door iseasily moveable and is often exposed in an uncontrolled way to theforces acting on it (gravity, springing of the suspension, dampers,etc.) when it is in an intermediate position between the closed and theopen position. When a spring of appropriate strength is present, afterthe opening of the clutch, tailgates are, as a rule, pivoted out of theintermediate position into the open end position, even though thevehicle door is often to remain standing in the respective intermediateposition for safety reasons.

The object on which the invention is based is to specify a clutch of thetype initially mentioned, by means of which what is achieved in a simpleway is that the vehicle door is held reliably in any intermediateposition when the clutch is in its disconnected state. Moreover, thepossibility of being able to carry out a manual emergency actuation ofthe vehicle door is to be preserved.

This object is achieved, according to the invention, by means of thefeatures of claim 1. Further, particularly advantageous refinements ofthe invention are disclosed in the subclaims.

The invention is based essentially on the idea of providing an elasticelement, for example a compression spring, which acts upon the armaturedisk of the clutch in the axial direction, in such a way that, with theclutch in the disconnected state, the armature disk is pressed againstthe friction lining of the rotor part with a force which is sufficientlyhigh to ensure that the vehicle door remains standing reliably in therespective position assumed during the disconnection of the clutch, andin such a way that, during a subsequent manual actuation of the vehicledoor, the frictional connection between armature disk and frictionlining can be overcome.

The invention has the advantage that the gap dimensional setting, whichis relatively complicated when conventional clutches are used, isdispensed with completely. Moreover, because of the preloading by meansof the spring, the clutch, in the connected state, can transmit a highertorque than a comparable clutch without preloading.

In a first embodiment of the invention, the second shaft is connectedfixedly in terms of rotation on the outside to a driver part comprisingaxial guide parts which engage into corresponding slot-like recesses ofthe armature disk. Advantageously, the driver may also have at least oneblind hole bore, open on the side facing the armature disk, forreceiving the compression spring used as an elastic element.

In order to achieve a space-saving arrangement of the clutch, there isprovision, in a second embodiment of the invention, for one of the twoshafts to be designed as a hollow shaft, into which the other shaft ineach case projects at least partially and by which this shaft is thenguided radially. In this case, the shaft designed as a hollow shaft maycarry on the outside a gearwheel or worm wheel which is operativelyconnected to the drive motor via drive elements.

In a further embodiment of the invention, there is provision for thehousing surrounding the clutch to be designed in such a way that itadditionally comprises both a gear stage following the clutch, fordriving a drive lever actuating the vehicle door, and a gear stage whichprecedes the clutch and via which the clutch is connected to the drivemotor flanged to the housing. By means of this measure, it is possiblein a simple way to construct the entire drive for actuating the vehicledoor as a prefabricatable module.

To adapt the clutch according to the invention to different motorvehicles or vehicle types, it is often necessary merely to exchange thespring which presses the armature disk against the friction lining.

Further details and advantages of the invention may be gathered from thefollowing exemplary embodiments explained with reference to figures, ofwhich:

FIG. 1 shows a diagrammatic side view, illustrated partially in section,of a drive unit for an automatic vehicle door with a clutch according tothe invention, and

FIG. 2 shows an exploded illustration of the clutch reproduced in FIG.1, the individual parts of the clutch being illustrated in perspective.

In FIG. 1, 1 designates a drive unit for the automatic actuation of atailgate, not illustrated, of a motor vehicle. The drive unit 1comprises an electric motor 2 which is flanged to a housing 3. Theelectric motor 2 is connected, via a worm gear unit 4 arranged in thehousing 3 and via an electromagnetic friction clutch 5 according to theinvention, to a two-stage epicyclic gear unit 6 which acts on apivotable drive lever 7. The drive lever 7 is connected fixedly in termsof rotation to a hinge strap, not illustrated, of the tailgate andcauses the closing of the latter insofar as the electric motor 2 is liveand the clutch 5 is closed.

The clutch 5 comprises a hollow shaft 8 which is provided, in the regionof its first end, with a worm wheel 9, into which the worm 10 of theworm gear unit 4 engages. The hollow shaft 8 carries, in the region ofits second end, a driver part 11, on which four guide parts 12 extendingin the axial direction are arranged. These guide parts 12 engage intocorresponding recesses 13 of an axially displaceable armature disk 14which, however, is connected fixedly in terms of rotation to the hollowshaft 8.

The clutch 5 comprises, furthermore, a shaft 15 which carries acup-shaped rotor part 16 which is connected fixedly in terms of rotationto the latter and which, on its end facing the armature disk 14, has afriction lining 17. That region 15′ of the shaft 15 which lies in frontof the rotor part 16 is led through the hollow shaft 8 and is guidedradially by the latter. Arranged fixedly in terms of rotation on theopposite end of the shaft 15 is a gearwheel 18 which cooperates with theepicyclic gear unit 6.

Located in a recess 23, on that side of the cup-shaped rotor part 16which faces away from the friction lining 17, is a coil 19 which isarranged fixedly with respect to the housing and the electricalconnections of which are designated by 20.

According to the invention, then, there is provision for the armaturedisk 14 to be pressed constantly against the friction lining 17 by meansof compression springs 21 which are mounted in corresponding blind holebores 22 of the driver part 11 or of the hollow shaft 8. In this case,the spring constants of the compression springs 21 are selected suchthat, with the clutch 5 in the disconnected state, the armature disk 14is pressed against the friction lining 17 of the rotor part 16 with aforce which is sufficiently high to ensure that the tailgate remainsstanding reliably in the respective position assumed during thedisconnection of the clutch 5, and such that, during a subsequent manualactuation of the tailgate, the frictional connection between armaturedisk 14 and friction lining 17 can be overcome, so that, in the event ofmanual emergency actuation, no appreciable load and therefore also noappreciable wear of the worm gear unit 4 or electric motor 2 occur.

The invention, of course, is not restricted to the exemplary embodimentdescribed above. Thus, for example, the electrical coil 19 does notnecessarily need to be arranged fixedly with respect to the housing.Instead, it may also be connected fixedly in terms of rotation to therotor part 16, insofar as its connections 20 are connected tocorresponding slip rings arranged on the rotor part 16 or the shaft 15.

The compression springs 21 may also be, for example, pneumatic springsor other elastic parts.

Moreover, the shaft carrying the rotor part does not necessarily have tobe mounted in a hollow shaft, but, instead, in the case of anappropriate mounting, the two shafts of the clutch may also be arrangedaxially one behind the other and consist, for example, of a solidmaterial.

LIST OF REFERENCE SYMBOLS

-   1 Drive unit-   2 Electric motor, drive motor-   3 Housing-   4 Worm gear unit, gear stage-   5 Clutch-   6 Epicyclic gear unit, gear stage-   7 Drive lever-   8 Hollow shaft, second shaft-   9 Worm wheel-   10 Worm-   11 Driver part-   12 Guide part-   13 Recess-   14 Armature disk-   15 Shaft, first shaft-   15′ Region-   16 Rotor part-   17 Friction lining-   18 Gearwheel-   19 Coil-   20 Connection-   21 Compression spring, elastic element-   22 Blind hole bore-   23 Recess (rotor part)

1. Electromagnetic friction clutch for a vehicle door or a vehicleaccess cover, for arrangement inside a driveline connecting a drivemotor (2) and one of a vehicle door and a vehicle access cover,comprising a clutch (5), which is arranged in a housing (3), said clutch(5) comprising a rotor part (16), which is provided with a frictionlining (17) and is rotationally locked to a first shaft (15), and onwhich an electrical coil (19) is arranged on a side remote from thefriction lining (17), and an armature plate (14) which is rotationallylocked to but axially displaceable on a second shaft (8) and which whenthe clutch (5) is energized is drawn against the friction lining (17) ofthe rotator part (16) on the first shaft (15), establishing a frictionalconnection between the two shafts (8, 15), wherein the armature plate(14) is acted upon in an axial direction by at least one elastic element(21), in such a way that when the clutch (5) is de-energized thearmature plate (14) is pressed against friction lining (17) of the rotorpart (16) with a force which in operation is sufficient to maintain thevehicle door or the vehicle access cover securely in the respectiveposition assumed when the clutch (5) was de-energized, and that thefrictional connection between the armature plate (14) and the frictionlining (17) can be overcome on subsequent manual operation of thevehicle door or vehicle access cover.
 2. Clutch according to claim 1,wherein the elastic element (21) is a compression spring.
 3. Clutchaccording to claim 1, wherein externally the second shaft (8) isrotationally locked to a carrier part (11), which comprises axial guideparts (12), which mesh in corresponding groove-shaped recesses (13) inthe armature plate (14).
 4. Clutch according to claim 3, wherein thesecond shaft (8) or the carrier part (11) contains at least one blindhole (22), open on the side facing the armature plate (14), forreceiving the compression spring (21).
 5. Clutch according to claim 1,wherein one of the two shafts (8, 15) takes the form of a hollow shaft(8), into which the other shaft (15) at least partially extends andwhich guides the other shaft (15) radially.
 6. Clutch according to claim5, wherein the shaft which takes the form of a hollow shaft (8)externally supports a gear wheel or worm wheel (9), which is operativelyconnected by way of drive elements to the drive motor (2).
 7. Clutchaccording to claim 1, wherein the rotor part (16), on said side remotefrom the friction lining (17), has a recess (23), in which the coil (19)is at least partially arranged.
 8. Clutch according to claim 1, whereinthe coil (19) is supported by being fixed to the housing.
 9. Clutchaccording to claim 1, wherein the clutch (5) is arranged in a housing(3), which in addition comprises at least one gear stage (6) connectedto the output side of the clutch (5) for driving an actuating lever (7)operating the vehicle door, and a gear stage (4) connected to the inputside of the clutch (5), by way of which the clutch (5) is connected tothe drive motor (2), flange-mounted on the housing (3).